Electrostatographic apparatus use electrostatically charged toner particles to develop electrostatic images on an imaging member. Charged toning particles are applied to the electrostatic image at a toning station. The developed images are then transferred to a receiving sheet. The quality of the toner image produced by such apparatus is substantially affected by the charge on the toner.
One class of toning stations controls the charge and presentation to the imaging member of the toner particles through the use of two component developers in which one component is the toner and the other is a particulate carrier, for example, a magnetic carrier. The charge on the toner particles is generated by triboelectrification of rubbing against the carrier particles.
In order to provide a stable charge over the relative humidity range to which such devices are exposed, it is proposed in U.S. Pat. No. 5,701,550 filed in the name of Loftus et al, the contents of which are incorporated herein by reference, to provide a heater surrounding the toning station. The heater acts as a supplementary source of heat and thus control of relative humidity in the developer station, particularly for use at times when the development station's rotatable magnetic core is not rotating, for example, when the copier/printer apparatus is off, at idle or at rest. When the toning station's rotatable magnetic core is operating, tribocharging of the toner particles is occurring and then will cause the toner charge to mass ratio to increase or decrease, depending upon type of toner, to a level suitable for acceptable performance. With two component developers, the lower limit of the charge to mass ratio (Q/m) for acceptable performance is most often defined by contamination of the device by toner dust as a result of low charge toner particles being thrown from the developer. The presence of toner of low Q/m may also provide unacceptable tone scale in image rendition. The upper limit to the charge level at which performance is acceptable may be due to limits of the latent image forming process on the photoconductive image member or to artifacts produced at high toner charge levels during transfer of the toned image to a receiver or to pick up of developer (carrier) in the image background.
In a copier/printer apparatus it is important to have ready availability of the apparatus for making of copies or prints. Where the copier apparatus is turned off, say overnight, or is subject to an auto cycle-off due to nonuse, the production of the first copy will depend upon the ability of the apparatus to restore the toner particles to within the appropriate Q/m range and for the apparatus to proceed with its set-up routine to determine that the various stations are functioning properly and their electrophotographic (EP) processing set points are appropriately set. If a heater is associated with the toning station and is heating during idle time of the apparatus the problem of relative humidity affecting Q/m of the toner is reduced. The set-up routine can then proceed appropriately as the apparatus cycles-up for readiness for printing or copying. A problem arises, however, when various malfunctions associated with the heater are detected. For example the heater may be determined to be not functional or a thermistor control therefor is determined not to be operative or the temperature of the development station is determined to be above set point and the heater is on but should not be on, or the temperature is below the temperature set point for the development station and the heater is off but should be on. Such problems can affect the ability of the toner in the toning station to reach charge equilibrium, i.e. settle within a Q/m range suited for imaging.
It is an object of the invention to provide a copier/printer apparatus and method which provides for a controlled auto set-up routine that accommodates errors associated with the heater of the toning station so that first copy or print availability is efficiently controlled.